The present invention relates to a clutch disc assembly used in a vehicle.
The clutch disc assembly is interposed between an automotive engine and an automotive transmission. The clutch disc assembly is used to connect or disconnect the power transmission and also to dampen torsional vibration as a damper. In general, the clutch disc assembly includes a hub connectable to an input shaft of the transmission and having a flange on its circumference, a pair of disc-like plates rotatably mounted on the hub and disposed on both sides of the flange, friction members fixed to the dlsc-like plates for frictional engagement with an input side rotary member such as the engine flywheel, coil springs used as elastic members for elastically coupling the disc-like plates and the flange in the circumferential direction, and a frictional resistance generation mechanism interposed between the disc-like plates and the flange.
In this clutch dlsc assembly, when torsional vibration is transmitted from the flywheel thereto, the coil springs are repeatedly compressed and expanded so that the pair of disc-like plates and the hub are twisted relative to each other. During this angular movement of the disc-like plates and the flange relative to each other, frictional resistance is generated on the basis of the frictional resistance mechanism, to thereby dampen energy of the torsional vibration.
In such a clutch disc assembly, in order to effectively dampen the torsional vibration over a wide operational range, it is preferable that magnitude of the frictional resistance be varied depending upon the kinds of the torsional vibration. There are two kinds of torsional vibrations, for example, torsional vibration having small angular displacement caused by the combustion fluctuation of the engine, and low-frequency torsional vibration having large angular displacement which is caused when a driver suddenly depresses or loosens an accelerator pedal. In order to dampen the torsional vibration having small angular displacement, the clutch disc assembly has to have low rigidity/small resistance characteristics as a damper. In order to dampen the low-frequency torsional vibration having large angular displacement, the clutch disc assembly has to have a high rigidity/large resistance characteristics as a damper.
In the conventional clutch disc assembly, the two different torsional characteristics may be realized by using a structure where the two different frictional forces are generated depending on the different kinds of the torsional vibration. However, with the frictional resistance by the sliding movement of the frictional member, it would be impossible to increase the second stage frictional force to a satisfactory level. It would be therefore impossible to sufficiently dampen the low-frequency vibration.
Recently, automotive vehicles have been widely used on highways. Thus, frequency of the engagement/disengagement of a clutch has been decreasing recently because of more highway use. For this reason, when a service life of a clutch disc assembly as a whole is contemplated, a problem of wear of friction facings has become less important. Then, a service life of an elastic member support portion of the pair of disc-like plates is being raised. In other words, when the torsional vibration is generated, the elastic member is repeatedly expanded and contracted to thereby wear the support portion of the disc-like plates.